The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Currently, in the field of metal surface decoration, a gradient color is mainly obtained by coating or printing dyes directly on the surface of a metal work-piece. However, a conventional surface decoration layer is usually a paint film. The paint film has a poor bonding ability with metals, thus the paint film peels easily. In addition, the paint film has a low hardness; therefore, the paint film may be worn and scratched easily.
Therefore, a method for decorating a metal surface is proposed, that is, treating a metal substrate having an anodic oxidation layer with dyes, in which dye molecules penetrate into micropores of the anodic oxidation layer. The dyed metal substrate has a surface different from the paint film, thus the dyed metal substrate having the anodic oxidation layer has a better metal texture and better surface properties. However, the color-gradience obtained is simple and lack of variety, i.e., the dye surface shows only a simple one-direction “linear” color-gradience, such as one color changing from dark to light or from light to dark, or a color changing to another different color.